Put a video game on the Nintendo 3DS and weird things can happen, including random pirate battles.

With Game Developers Conference ramping up around me in downtown San Francisco today, I walked into a hotel and briefly tried Lego Pirates of the Caribbean 3DS. Sure, there are game developers to talk to around here, but there are also games to check out and the irresistible allure of seeing what people are doing with Nintendo's new handheld.

For experienced eyes like mine, Lego Pirates of the Caribbean's glasses-free 3D was a familiar feat. I've seen a couple dozen 3DS games in the last year for Nintendo's new handheld. The 3D in this game is subtler than most, designed not to tire young eyes by putting the focal point of the 3D on the player's character. The background pops or recedes around him; collected Lego studs shoot toward the player in 3D.

That's well done but unsurprising.

The 3DS has other tricks, though, and the 3DS version of Lego Pirates, a port of the standard DS game with better lighting and character models pulled from the Wii version, uses the system's quirkier features.

It uses Play Coins, the currency 3DS owners earn for taking steps in real life while they carry the system. You walk with the 3DS, you gain coins. As in Sega's Super Monkey Ball 3D, you can use them to unlock some of the game's characters.

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Like Capcom's Super Street Fighter IV for 3DS, the game also uses the 3DS Street Pass feature. That lets a game owner set up a pirate character who will automatically battle other3DS owners' pirates, should the system owners pass each other while the systems are in sleep mode (the game need not be in the machine).

A player has some control of how their pirate will fare during these accidental encounters. They can set up three attack moves and three defense moves, all affected by a rock-paper-scissors dynamic. Two pirates battling through Street Pass will essentially have their owners' pre-set moves matched against each other and the systems will sort out who wins. When those 3DS owners check their system with a copy of the game in it, they will be able to see how their pirate did and be able to watch a replay of the conflict. For any victories, they will earn coins that can be spent unlocking other characters.

It's not a game-selling feature, but the Street Pass is a nice perk, one that seems popular with 3DS game makers. I expect to see much more of it, given the early enthusiasm creators seem to have for it.

(Note: I don't have 3DS screenshots to show you, so you're getting Lego Pirates concept art up top instead. The 3DS game looks nicer than a DS game but certainly not the caliber of the Xbox 360 version that I also glimpsed today.)